Structural and electrical transport properties of a rare earth double perovskite oxide: Ba2ErNbO6

The double perovskite oxide barium erbium niobate, Ba2ErNbO6 (BEN) was synthesized by solid state reaction technique. Rietveld refinement of the X-ray diffraction pattern of the sample showed cubic (Fm3m) phase at room temperature. Fourier transform infrared spectrum showed two primary phonon modes of the sample at around 387 and 600 cm−1. Raman spectrum of the sample taken at 488 nm excitation wavelength showed four primary strong peaks at 106, 382, 747 and 814 cm−1. Lorentzian lines with 10 bands were used to fit the Raman spectrum. A group theoretical study was performed to assign all the Raman modes. Impedance spectroscopy was applied to investigate the ac electrical conductivity of BEN in a temperature range from 303 to 673 K and in a frequency range from 100 Hz − 1 MHz. The dielectric relaxation mechanism was discussed in the frame work of permittivity, conductivity, modulus and impedance formalisms. The complex plane plot of the impedance data was modeled by an equivalent circuit consisting of two serially connected R-CPE units, (one for the grain and the other for the grain boundary), each containing a resistor (R) and a constant phase element (CPE). The R-CPE units were used to incorporate the non-ideal character of the polarization phenomenon instead of an ideal capacitive behaviour. The relaxation time corresponding to dielectric loss was found to obey the Arrhenius law with activation energy of 0.85 eV. The frequency dependent conductivity spectra followed the Jonscher power law. The Cole-Cole model was used to investigate the dielectric relaxation mechanism in the sample.